The present invention relates to determining an physical property of a device under test by optical reflectometry measurements.
For determining optical properties of an optical device under test (DUT), e.g. an optical fiber, it is known to apply a so-called optical time domain reflectometry (OTDR) or optical frequency domain reflectometry (OFDR). For that purpose an optical signal is coupled into the DUT, which travels along the DUT and which is partly scattered by the DUT, e.g. due to inhomogeneities in the silica structure (Rayleigh scattering) along the optical fiber or due to interaction of the optical signal with optical phonons (Raman scattering) or acoustical phonons (Brillouin scattering). Some of the scattered light travels back to the DUT input. The power of this returning light is measured and evaluated.
It is further known to separate different spectral components of the backscattered light from an optical fiber and to put these components into relation in order to obtain a physical property of the fiber. Well-known scatter signals returning at different wavelengths are so-called Raman scatterings. An arrangement for measuring a temperature distribution along an optical fiber by determining Raman scatterings is e.g. described in U.S. Pat. No. 5,618,108. The related technical background is e.g. described, in “Optical Fiber Communications” by J. Senior, Prentice Hall, 1992, pages 91-96.